Nakabusa Onsen Hot Springs

Visit Nakabusa Onsen Hot Springs for your experience of nature, mountains, history, and relaxation

After visiting Nakabusa Hot Spring more than 100 times over the past 20 years to study microorganisms in hot water, I became a favorite and feel more relaxed and energetic each time I visit. It is a beautiful place for those who want to enjoy a relaxing hot spring in old Japan, those who want to enjoy being in the forest, and those who want to feel the history of mountain areas in Japan since the Edo period.

Fantastic number of various hot springs indoors and outdoors

As far as I know, Nakabusa Hot Springs is the best in Japan in terms of the number of hot springs and the amount of hot water for a particular inn. Water constantly flows from various sources into 17 indoor and open-air baths. If you count the baths for men and women and those with multiple baths, the number is 27. In addition, the remaining hot spring water flows outdoors and is being used as our research site for microorganisms.

There are 5 mixed baths (3 with women-only hours), 3 private baths, and 4 separate baths for men and women. There is an outdoor stump bath for one person, a hot spring swimming pool, a footbath, a heat-ground bath, and a steam bath. On weekdays during the off-season, there are more bath facilities than guests. Even on weekends during the high season, if you assume everyone is in the bath at the same time, there are only about 4 people per bath on average, and in reality, the number is, of course, less at the same time. This alone will give you an idea of how relaxing and enjoyable a variety of baths can be.

Of the 17 baths, Neba no Yu and Family Bath are not introduced on the inn’s website. Fifteen or more is a large enough number anyway, so it may be thought that it is not an appealing point. Of course, everything is written on the bath map you receive when you stay.

I will briefly introduce the 17 baths along with my comments. I added the era I feel in my imagination (Edo, Meiji, Taisho, Showa, Heisei). Edo is more than 150 years old, and Heisei is the newest.

We will introduce the baths in order, starting with the ones in the back. I will also write down my favorites, numbers 1 to 6.

Shirataki no Yu (Meiji) (No. 1): This is an open-air bath directly connected to the source flowing down from the middle of a rock several meters above. A beautiful forest is on the opposite bank. It’s my favorite.

Goza no Yu (Meiji era): This indoor bath is where you can feel the most traditional style. Perhaps the image of Edo has also been inherited. The name comes from the Matsumoto feudal lord of the Edo period.

Furou-sen (Heisei) (No. 2): A bath with beautiful wood and rock created to suit modern tastes while emphasizing tradition. A large opening allows outside air to enter constantly so that you can enjoy a small forest bath. This is my second favorite. (There is a women-only time)

Oyu (Showa) (No. 6): There is a small open-air bath for men and women and an indoor bath downstairs. The starry sky and dawn are beautiful outdoors. Until Yubara no Yu was built, it was used by climbers coming down the mountain, so lockers remain in the changing room. This is my sixth favorite.

Dai-yokujo bath (Taisho): This is the largest indoor bath in the inn. The changing rooms are separate for men and women, but the inside is the same. As a child, I often saw baths with separate changing rooms for men and women in the NHK puppet shows “Chirorin Village and Kuruninoki.” This was a form of bathing when mixed bathing was the norm. (There is a women-only time)

Rock bath (Taisho) (No. 5): This is an open-air bath that is directly connected to the building, and the rock formations, blue sky and clouds, mountain slopes, and starry sky are beautiful. The changing room is small and unisex, and I can imagine what mixed bathing open-air baths used to be like in the past. This is my fifth favorite. (There is a women-only time)

Family bath (Showa era): Two separate baths can be locked and used for private use. It feels like a larger bathroom from home from 50 years ago, and to me, it smells like the Showa era. It’s usually empty.

Taki no Yu (Showa): This is a private open-air bath. There are two on the left and right. Although small, it is suitable for two or three people to use it calmly. There is a small cold-water tab next to the bath, so I used to keep the tub cool when my child was small. The hot water falls from a high place.

Wata no Yu (Heisei era): This footbath is a place where everybody can enjoy chatting. After microbial research with students, I often took this bath while eating boiled eggs made in a nearby hot water reservoir. It was fun. Before it was renovated into a footbath about 15 years ago, “Wata no Yu” had an Edo-era image, with only an open bathtub in the middle of an outdoor walkway and a bath that only those who wanted to take through all the baths could take.

Steam bath (Edo) (No. 4): You will be surprised by the sound of the hot spring boiling under the wooden drainboard floor. This is a steam bath where the steam flows smoothly, unlike the image of steam accumulating in a closed room. You can see the sky beyond the steam through the transparent panel roof. This is my fourth favorite.

Tsukimi no Yu (Heisei): This relatively new open-air bath has a great view of the sky and mountain slopes. Out of the three mixed open-air baths far from the inn, this is the closest to the building. I remember going there with my elderly parents as a family.

Nekkoburo (Heisei era): This bath is carved out of a large zelkova stump. Although it is designed for one person, it can also be used by two intimate people. You can see outside through the blinds, which is a rare experience.

Hot spring pool (early Showa era) (No. 3): This pool dates back to the early Showa era and is a registered tangible cultural property of the country. No other pools from that time remain in the country. When searching online, only one other swimming pool is registered as a cultural property, which is newer. Chloroflexus, a thermophilic photosynthetic bacterium we use in our research, often floats around. The water temperature is often too hot for swimming but suitable for bathing. From June to October, I swim every time I go. This is my third favorite.

Thermal ground lying (Edo): When you lie down on the ground, and warm steam on a drainboard and mat spread out, you feel very comfortable, and you can relax and gaze at the sky. The temperature and humidity vary depending on the location, so experiment before choosing a location. Early morning, evening, and night are recommended.

Neba no Yu (Heisei): This is the newest bath and seems to be made of particular cedar. It can be reserved. The quality of the hot springs here is strong, and someone wrote on her blog that she liked the quality of the hot springs the best in Nakabusa.

Yubara no Yu (Heisei): This bath is available for day trips right next to the Mt. Tsubaku trailhead. Inn guests can use the facility free of charge during their stay. There are two large baths for men and women, each with different water quality. The rocks and shrubbery are beautiful and large, so you can take your time. The genders change every day, so you can enjoy both if you stay overnight.

Bosatsu no Yu (Meiji period): This is an open-air bath that you enter into the forest from a little down away than Yubara-no-Yu. You will wonder why it is in such a place. A hot spring source is nearby, and I believe the bath has been built here for a long time. You can enjoy hot spring and forest bathing simultaneously, like Shirataki no Yu.

Relaxing surrounded by pleasant forests at Nakabusa Hot Spring.

Nakabusa Hot Spring is located at the eastern foot of Mt. Tsubakuro, in a slightly open area upstream of the Nakabusa River and Kassen River confluence. You will see a steep mountain slope if you go a little further away. The area around the inn is a natural forest, especially on the steep slopes, which are untouched forests.

Even though it is called an ancient forest, it is a bright forest with a mixture of various types of deciduous trees, evergreen trees, broad-leaved trees, and coniferous trees, with many larch and birch trees. In addition to larch and birch, there are Quercus oak, various Japanese maples, Mountain Cherry, and fir. Silabiso. Arborvitae, Japanese arborvitae, spruce, hemlock, cedar, and cypress are growing here. I wrote this while remembering the materials from the Forestry Agency’s protected forests in the Northern Alps and my field training in plant taxonomy during my university days.

If you come repeatedly, you may enjoy the surrounding forest’s ever-changing beauty. Each season brings a unique charm. In May, the forest is adorned with fresh greenery, its density and color evolving daily. By June, the green deepens, and the forest stabilizes, punctuated by the striking dark green of the coniferous trees.

From October to November, you can see a variety of autumn leaves, one after another. At first, maple treetops in sunny areas susceptible to radiative cooling turn red. The surrounding area is still green, but some places are bright red. There are several such maple trees right in front of Shirataki no Yu.

Eventually, the whole trees of maples, Quercus oaks, and other broad-leaved trees will change color. The autumn leaves of the ivy wrapped around the tree are also beautiful. Larch trees change color at the end of the season. Because there are so many trees, the mountain gradually turns gorgeous yellow, orange, and light brown.

Once most of the leaves have fallen, the white color of the birch trunk becomes noticeable, which is also beautiful. Around that time, due to road closures, Nakabusa Hot Spring will also be closed for the winter. There are keeper persons even in the winter, so you can stay overnight after walking 4 to 5 hours each way on snowy roads. The trees covered in hoarfrost and snow are magnificent.

I have written stories about Nakabusa’s forest from various aspects, but just one of them would be great. While soaking in a hot spring or looking at the surrounding forest while breathing slowly from the window or garden, your heart will be cleared, and you will feel happy. The contrast between the sky and clouds is beautiful, and the light and colors change subtly. Please come and immerse yourself in the rich forest of Nakabusa.

Experience the histories at Nakabusa Hot Spring

History of life since early days of earth

Let’s start with the history of life, which is my specialty. The prevailing theory is that the first living things to appear on Earth about 3.8 billion years ago were at temperatures of around 100 degrees Celsius in the ocean. This was because there was a lot of heat coming from the Earth itself, there was still heat left from the vast meteorites that frequently collided, and there was a large amount of carbon dioxide in the atmosphere, creating a strong greenhouse effect. The amount of heat from the sun is thought to be less than now.

At Nakabusa Hot Spring, high-temperature water naturally flows out from various spots. As the water flows, the temperature drops continuously from around 95°C to around room temperature. In this way, there are not many places in the world where hot spring water flows within a range of temperatures ranging from 95℃ to room temperature. We believe that temperatures between 95℃ and 50℃ reproduce the history of the Earth from 4 billion years ago to 2 billion years ago.　95℃ to 70℃ until about 3.3 billion years ago, 60℃ until about 2.7 billion years ago, and 50℃ until about 2.2 billion years ago.

In addition to temperature, the quality of the spring water at Nakabusa Hot Spring provides all the materials necessary for life, helping research into the history of life. Living things require various materials to survive, but carbon and electrons are especially needed in large quantities. The rice and bread we eat every day can obtain both carbon and electrons at the same time. Plants get carbon from carbon dioxide and electrons from water; because they lack energy, they use sunlight. The water at Nakabusa Onsen also contains carbon dioxide. Electrons are coming from hydrogen sulfide. Therefore, microorganisms can grow even in the absence of the sun and develop even better when there is sunlight.

The evolution of life being revealed at Nakabusa Hot Spring is intricately linked to temperature. At temperatures ranging from 95°C to 70°C, we find evidence of chemosynthetic bacteria dating back approximately 3.8 billion years. As the temperature drops from 70°C to 60°C, we encounter photosynthetic bacteria that utilize hydrogen sulfide, believed to have originated around 3.3 billion years ago. Finally, below 60°C, we observe photosynthetic bacteria from 2.7 billion years ago, including a cyanobacterium that uses water to supply electrons. By studying these bacteria and their communities at each temperature, we can gain insights into the history of life during the first half of Earth’s existence.

History of mountains of the Northern Alps and the birth of hot springs

The Japanese archipelago, which was attached to the Eurasian continent until about 20 million years ago, gradually separated from the continent with the birth of the Sea of Japan. By about 15 million years ago, the archipelago had become similar to the current “inverted dogleg” shape. However, until about 3 million years ago, the area around the Northern Alps and Nakabusa Hot Spring was not exceptionally high mountainous but rather hilly, with no volcanoes, hot springs, or granite at the surface.

Three million years ago, the moving direction of the Philpin Sea Plate changed from northward to northwestward, which caused significant east-west pressure to be applied to the entire Japanese archipelago. Energy derived from east-west pressure has caused uplift and increased volcanic activity on the west side of the Fossa Magna. This is the birth of the Northern and Southern Alps. In particular, active volcanic activity in the Hotaka/Yari/Tsubakuro mountain areas, including the Nakabusa Hot Spring, forms gigantic calderas and granite deep underground. I understand that the heat source of the activities from around this time created the source of the hot water at Nakabusa Hot Springs and that the thick Ariake granite older than 50 million years is one factor that determines the spring’s quality. Volcanic-like activities have been found in Io-Zawa, which is 7 km west of Nakabusa Hot Springs, and an active volcano, Yakedake, is located 16 km southwest of Nakabusa Hot Springs.

When high mountains are formed, surface erosion intensifies, the mountains become lighter, and underground rock masses slowly rise. Today, the granite around Mt. Tsubakuro and Nakabusa Hot Spring has been formed. The granite near Nakabusa Hot Spring has cooled and solidified deep underground, so the crystals are large and easily crumble. After collapsing, they become large grains of sand.

Hot springs in the mountains often rise to the surface along faults, clefts in large blocks of rock. When such faults exist, they are easily eroded by water flowing on the surface, which turns into rivers. Hot springs are more likely to flow where rivers meet, significantly because two faults overlap. Many hot springs naturally gush at such places as Nakabusa, a fascinating phenomenon that continues to pique my curiosity.

The hot springs and history of the inn

Many people began living in Azumino in the 6th century when a large clan from around Hakata, north of Kyushu, developed this area and called themselves the Azumino clan. Considering that some people probably went into the mountains for hunting and other activities around that time, I imagine they might have found Nakabusa Hot Spring and made them warm.

According to the inn’s website, the origins of what is now Nakabusa Onsen can be traced back to the inn’s website: “The use of hot springs in recent years began in 1821 when the Matsumoto Domain ordered Mohachiro Momose to collect alum to create a luster to raw silk”. He entered this area to collect the alum needed for this and began mining alum and building a hot water hut. The access route at this time was not the current road along the river but the access route up Shinano slope from the south over the ridge pass.

The Momose family did their best to prevent the right to hot springs from being taken away during the early Meiji era. The subsequent development followed as a mountain climbing base and resort during the Meiji and Taisho eras. I learned there was a tennis court and a pool in early Showa when I bought a postcard with a photo reproduction from that time.

I heard one of the grandmothers, whose bust is erected in the garden, studied at Tokyo Sixth Girls’ High School (now Tokyo Metropolitan Mita High School). The old building was the In-forest summer Dormitory of the 6th High School at the time. I imagine the notice that can still be read at the entrance, “Sitabakino Mamade Oagarini Naranu Koto, meaning do not enter with outdoor shoes,” dates back to that time. I stayed at Nakabusa Onsen for the first time in 2002. After returning to Tokyo, I told my father, who loved mountains, that around 1930, when my father was around 20 years old, he mountaineered from Mt. Yarigatake through Omote Ginza, descended to Nakabusa Hot Spring, and stayed there. At that time, he said that there were many female students from the 6th Prefectural High School. When I took my parents to Nakabusa Hot Spring with my family in the fall of that year, he was pleased and nostalgic.

People who recommend Nakabusa Hot Spring and who don’t

As introduced above, Nakabusa Hot Springs is a place where you can enjoy hot springs, forests, and history in a very relaxed manner. However, since it is an old inn deep in the mountains, it may be a place that not everyone can enjoy. Although it is my opinion, I will write about the people who recommend Nakabusa Hot Springs and those who do not.

People I do recommend

who want to enjoy many hot spring baths
who want to enjoy slight differences in spring quality
who want to enjoy hot springs in a natural forest
who want to enjoy hot springs while feeling the history
who want to enjoy hot springs in a quiet atmosphere
who want to enjoy seeing the rich virgin forest around them
who want to enjoy buildings and facilities from the late Edo period, Meiji, Taisho, Showa, and Heisei periods.
who want to relax in nature
who have no problem with some old facilities or simple customer service
who don’t have a problem with high humidity in mountain valleys or the presence of insects outdoors

People I don’t recommend

who hate hot springs
who want to enjoy a variety of vastly different spring qualities
who expect something other than hot springs, forests, history, mountains, and relaxation.
who expect all new and clean facilities
who expect excellent customer service
who expect food like a luxury Japanese inn
who are very afraid of insects and humidity
who have a program they want to watch on terrestrial TV
who want to enjoy games and karaoke
who hate to back up once or twice on the mountain road and pass each other if you come by car

If you fit into two or three of the above-recommended points, you’ll fall in love with Nakabusa Onsen and want to go again. Even if some of my recommendations don’t apply to you, going there is okay.

Just so you know, some of the Lodge’s facilities are old, but you will tolerate them if you stay there, thinking of it as a mountain hut or an old hot spring resort. If you need more comfort, I recommend Shosenkaku, a regular inn.

In the spring and summer of 2021, four rooms at the lodge, Ume 1 to Ume 4, were renovated and now feature toilets and sinks. Though simple, the interior of the room has been beautifully finished by a carpenter. I recommend the Lodge room with a toilet if you prefer easy meals. The view of the Nakabusa River and the trees in the forest from these rooms is also a sight to behold, adding to your comfort and enjoyment.